1. Technical Field
The present disclosure generally relates to well bore tools and in particular to apparatus and methods for detecting a substance in a downhole fluid.
2. Background Information
Drilling tools and wireline tools are used to reach and evaluate subterranean formations that produce oil and gas. These tools often incorporate various sensors, instruments and control devices in order to carry out any number of downhole operations. The operations may include formation testing, fluid analysis, and tool monitoring and control.
Information about the subterranean formations traversed by the borehole may be obtained by any number of techniques. Techniques used to obtain formation information include obtaining one or more downhole fluid samples produced from the subterranean formations. Downhole fluids, as used herein include any one or any combination of drilling fluids, return fluids, connate formation fluids, and formation fluids that may be contaminated by materials and fluids such as mud filtrates, drilling fluids and return fluids. Downhole fluid samples are often retrieved from the borehole and tested in a rig-site or remote laboratory to determine properties of the fluid samples, which properties are used to estimate formation properties. Modern fluid sampling also includes various downhole tests to estimate fluid properties while the fluid sample is downhole.
Some formations produce hazardous fluids, such as hydrogen sulfide and other gases that may damage tools, present safety hazards to surface personnel, and that may reduce the viability of the formation for producing useful hydrocarbons. Surface testing for these fluids requires bringing the fluid to the surface. For H2S gas measurement, unless one is careful in the selection of sample tank material, retrieval of a sample to the surface runs the risk of under-reporting the actual H2S levels. The reason is that H2S chemically reacts with many materials. The unreacted, remaining amount of H2S in the sample that is finally measured at the surface may be significantly less than the total amount of H2S that had been in the original sample so that the H2S concentration gets under reported. That is another reason that an in-situ measurement is preferable. However, an in-situ measurement of the chemical composition of these fluids presents unique problems due to the rigorous downhole environment.
The environment in a well presents many challenges to maintain the tools used at depth due to vibration, harsh chemicals and temperature. Temperature in downhole tool applications presents a unique problem to these tools. High downhole temperatures may reach as high as 392° F. (200° C.) or more making it difficult to operate sensitive electronic components in the environment. Space in a downhole carrier is usually limited to a few inches in diameter. Cooling systems typically utilize large amounts of power and take up valuable space in the tool carrier and add an additional failure point in the system.